Basic phenates to inhibit silver corrosion in thiophosphate-containing lubricating oils



atented tiuiy 1%, i55

2,713,557 EASIC PHENATES TO INEEIT SILVER CGRRO- SIGN IN THIUPHQSPHATECGNTAINTNG LUBRE- CATING OILS Warren Lowe, Berkeley, Calif., assignor to California Research Qorporation, San Francisco, Calirl, a corporation of Delaware No firawing. Application December 6, 1951, Serial No. 260,34G 13 Claims. (Ci. 25232.7)

This invention pertains to lubricating oil compositions resistant to oxidation and noncorrosive to silver and like In particular, this invention pertains to lubricating oil compositions containing zinc and calcium salts of mixed diesters of dithiophosphoric acids and basic calcium and barium salts of alkyl phenols.

Metal salts of dialkyl dithiophosphoric acids (wherein the alkyl groups are the same and of high molecular weight) were proposed for use in lubricating oil compositions to inhibit oxidation thereof. Although these metal salts of high molecular weight dialkyl dithiophosphoric acids are effective for the intended purpose, it was desirable to improve the oil solubility and to decrease the cost of these lubricating oil oxidation inhibitors. It

substituted for the high molecular Weight dialkyl dithiophosphates, and in addition were cheaper. In the search for still less expensive thiophosphates, the metal salts of dialkyl dithiophosphoric acids wherein the alkyl groups contain 6 carbon atoms or less (e. g., 4 carbon atoms) were considered. Although attractive because they were less expensive than the aromatic dithiophosphate, these loW molecular Weight dialkyl dithiophosphates do not have sufficient oil solubility to prepare concentrated solutions in oil. Thus, they could not be satisfactorily employed commercially. Therefore, those dialkyl dithiophosphates did not solve the problem of finding a less expensive but highly oil-soluble dithiophosphate which could be incorporated into lube oil compositions in large quantities. Consequently, the aromatic dithiophosphates continued to be used, and have been used these salts were sulficiently oil-soluble for the preparation of concentrates. In these mixed diesters of dithiophosphoric acids, the ester groups are derived from two different low molecular weight alcohols. For example, one of the radicals may be an alkyl radical containing 4 carbon atoms, and the other ester group may be an alkyl radical containing 6 carbon atoms.

Although these zinc (or calcium) salts of mixed diesters of dithiophosphoric acids are highly satisfactory in substantially all respects, including high oxidationinhibiting properties and good oil-solubility, they unfortunately fall down in one respect; they are corrosive to silver bearings. i t is thus essential to overcome this corrosion to silver caused by these salts of mixed diesters of dithiophosphoric acids.

The attack on silver by metal salts of mixed diesters of dithiophosphoric acids is believed to be due to the sulfur present. This corrosion may be designated as sulfur corrosion in contrast to the well-known oxidation corrosion caused by the action of acids and peroxides which are found in lubricating oils as combustion products of motor fuels and as products of oxidation of lubricating oils. Oxidation corrosion (or acid corrosion), adversely affects such hard metal alloys as ill) ill

, phenol.

nice 2 cadmium-silver, copper-lead, etc., but does not seriously affect silver or bronze. Such oxidation corrosion is readily inhibited by the low molecular weight dithiophosphates, as noted hereinabove. Unfortunately, these oxiration inhibitors which inhibit oxidation corrosion of cadmium-silver alloys severely corrode silver metal due to the presence of sulfur.

It is not contemplated herein that the silver which is attacked by the sulfur be a constituent of an alloy containing only small amounts of silver, as, for example, the silver in cadmium-silver alloy. Where an alloy containing small amounts of silver is used, the sulfur normally present in lubricating oil additives is not corrosive to such an alloy.

Corrosion of silver is'becoming an important problem for lubricants because of the increased use of silver as a wearing surface metal. Silver is being employed for bearings due to its high resistance to wear, under extreme pressure, bearing loads and speeds of todays engines, particularly in railroad diesel engines and in aircraft engines. Because the silver surfaces (e. g., silver wrist pin bushings) are susceptible to this attack by the sulfur of sulfur-containing lubricating oil additives, there has been a tendency to eliminate highly effective sulfurcontaining additives from diesel and aircraft engine lubricating oils, thereby losing the remarkable benefits of these additives. it has been the practice to forego the benefits derived from sulfur-containing additives and substitute in place thereof somewhat inferior compounding agents which would permit the oil to deteriorate more rapidly through oxidation, but saving the silver wearing surfaces.

It is a primary object of this invention to prepare :lubricating oil compositions which are stable to oxidation and at the same time resist corrosion to silver and like metals.

It is another object of thisinvention to reduce the corrosion to silver caused by lubricating oil compositions containing zinc or calcium salts of mixed esters of dithiophosphoric acids, wherein the ester groups are obtained from two dissimilar alcohols.

These and other objects of this invention will be apparent from the ensuing description and the appended claims.

According to the present invention, the corrosion to silver caused by lubricating oil compositions containing zinc or calcium salts of mixed esters of dithiophosphoric .acids having two dissimilar low molecular Weight ester groups can be inhibited by the addition of basic phenatesto the lubricating oil composition. Lubricating oil compositionshaving these metal salts of mixed esters of dithiophosphoric acids incorporated therein to inhibit oxidation corrosion are corrosive .to silver metal; however, this corrosion to silver can be inhibited by the additionof basic phenates to such lubricating oil compositions. The lubricating oil compositions of this invention comrise a major proportion of an oil of lubricating viscosity, and minor amounts of salts of mixed esters of dithiophosporic acids and basic sulfurized metal salts of It is preferred that the basic phenates be present in less amounts than-the metal salts of mixed esters of dithiophosphoric acids.

Suitable base oils include a wide variety of lubricating oils such as naphthenic base, paraflin base, and mixed base mineral oils, other hydrocarbon lubricants, e. g., lubricating oils derived from coal products, and synthetic oils,

. e. g., alklyene polymers (such'as polymers of propylene,

butylene, etc., and mixtures thereof), alkylene oxide type polymers, dicarboxylic acid esters, liquid esters of acids of phosphorus and silicon, alkyl benzene polymers, polysiloxanes, etc. Synthetic oils of the alkylene oxide type polymers which may be used include those exemplifled by the alkylene oxide polymers (e. g., propylene oxide polymers) and derivatives, including alkylene oxide polymers prepared by polymerizing alkylene oxides, e. g., phosphoric acids are excellent lubricating oil additives propylene oxide, in the presence of water or alcohols, for inhibiting corrosion of copper-lead and cadmium.- e. g., ethyl alcohol, and esters of alkylene oxide type silver bearings resulting from oxidation. The corrosion polymers, e. g., acetylated propylene oxide polymers of the copper-lead and cadmium-silver bearings resultprepared by acetylating propylene oxide polymers coning from oxidation corrosion, however, is not the same taining hydroxyl groups. type of corrosion resulting to silver wearing surfaces- Synthetic oils of the dicarboxylic acid ester type inwhen metal salts of mixed diesters of dithiophosphoric elude those which are prepared by esterifying such diacids are present. carboxylic acids as adipic acid, azaleic acid, suberic acid, It has been discovered that the corrosion to silver sebacic acid, alkenyl succinic acid, fumaric acid, maleic caused by lubricating oil compositions containing metal acid, etc., with alcohols such as butyl alcohol, hexyl salts of dithiophosphoric acids is inhibited by incorporatalcohol, 2-ethyl hexyl alcohol, dodecyl alcohol, etc. ing therein basic sulfurized metal salts of phenol.

Examples of dicarboxylic acid ester synthetic oils in- As used herein, the term phenol means phenol and clude dibutyl adipate, dihexyl adipate, di-Z-ethyl-hexyl derivatives of phenol; similarly, the term metal phenate S acate, di-n-heXyl fumaric polymer, etc. means the calcium and barium salts of phenol and de Synthetic oils of the alkyl benzene type include those rivatives of phenol.

which are prepared by alkylating benzene (e. g., dodecyl The term basic sulfurized metal phenates (e. g.,

benzene, tetradecyl benzene, etc.). basic sulfurized calcium hexadecyl phenate) means metal Synthetic oils of the type of liquid esters of acids of phenates having metal contents from 10% to 100%- phosphorus include the esters of phosphoric acid, e. g., and greater than 100% in excess of the amount of metal tricresyl phosphate; the esters of phosphonic acid, e. g., present in the corresponding sulfurized normal (or neudiethyl ester of decane phosphonic acid. etc. tral) polyvalent metal phenates.

Synthetic oils of the type of the liquid esters of silicon The basic sulfurized p ly metal phen s ar oil and the polysiloxanes include those exemplified by tetra soluble, and are derived from phenols which contain from. (2-ethylhexyl) silcate, hexa (4-methyl-2-pentoxy) disill to 5 cyclic, straight-chained or branched-chained, satu oxane, tetra 4-rnethyl-2-pentyl) silicate, tetra (1,3-dirated, or unsaturated, essentially hydrocarbonaceous radmethylbutyl) silicate, poly-methyl phenyl siloxane, polyicals having from 4 to carbon atoms, attached to the methyl siloxane, etc. benzene ring. It is preferred to use phenols having an The salts of mixed diesters of dithiophosphoric acids alkyl radical attached to the benzene ring, said alkyl radiused according to this invention are represented by the 30 cal containing from 10 to 18 carbon atoms. following formula: Examples of suitable essentially hydrocarbonaceous rads icals include alkyl radicals such as butyl, hexyl, octyl, decyl, dodecyl, hexadecyl, eicosyl, triaconityl radicals; radicals derived from petroleum hydrocarbons, such as R 2 white oil, wax, olefin polymers (e. g., polypropylene and polybutylene, etc.

Examples of metal phenates include the calcium and barium salts of octyl phenol, decyl phenol, dodecyl phenol, tetradecyl phenol, hexadecyl phenol, trianconityl phenol, etc.

The effectiveness of a particular basic sulfurized metal phenate for inhibiting silver corrosion of a lubricating oil composition according to this invention is somewhat dependent upon the amount of metal present in excess of that necessary for a neutral (normal) sulfurized metal phenate. As noted in comparing the data presented hereinbelow in Tables I and HI, 0.25 millirnole percent of the basic phenate of Example 4 (wherein the basic phenate had 45% more calcium than that required for forming a wherein R and R are dissimilar alkyl radicals, and M represents a metal selected from the group of zinc and calcium.

In the practice of this invention, it is preferred to use zinc and calcium salts of mixed diesters of dithio- 40 phosphoric acids wherein R of the above formula represents an alkyl radical containing not more than 4 carbon atoms, which includes the following radicals: methyl, ethyl, propyl, isopropyl, butyl, sec.-butyl, tert.-butyl, etc.; and wherein R represents an alkyl radical containing from 6 to 10 carbon atoms, which includes the following radicals: hexyl ethylisobutylmethyl, methylisopropylmethyl, heptyl, isoheptyl, 2-ethyl amyl, octyl, isooctyl, 3-ethyl hexyl, 2-propyl amyl, decyl, etc. Because of the increased silver protection derived therefrom, it phenat?) was more fi l reducmg sulfur is particularly preferred to use the, Zinc salt 0f mixed corrosion to silver than 0.25 mnlimole percent of the diesters of dithiophosphoric acids where R represents a baslc Phenata of Exefmple 6 (Wherem h baslc phenfite' butyl radical and represents a hexyl radical. had 85% more calcium than that required for forming The metal salts of dithiophosphoric acids are still efa neutral ph fective for the purposes of this invention when R of 5.. The suifunmd metal phenates can be P p the above formula represents alkyl radicals containing by a Process involving the use of y Glycols which up t 18 carbon atoms; 6, g the radicals; undecyl can be used as the solvent to prepare sulfurized basic d l tetradecyl hexadecyl, octadecyl, em metal phenates of this invention may contain up to 6 car- The diesters of dithiophosphoric acids used in the hon atoms- Suitabla glycols include: ethylene hp preparation of the zinc and calcium salts of this inven- (3f Py glycol, hlltahe Pentane h tion include the following: butyl hexyl dithiophosphoric methyl butane (11016.4- Becauseof the hlgher yleld o acid, methyl hexyl dithiophosphoric acid, ethyl hexyl diproduct obtained, ethylene glycol is the preferred solvent.

thiophosphoric acid, isopropyl rnethylisobutylcarbinol di- Basic Sulfufiled metal phenates y be P p from thiophosphoric acid, butyl rnethylisobutylcarbinol dithionormal metal alkyl phenates Or from p when phosphoric a id, b t l heptyl di hi h h i id butyl phenols are used as the starting materials, phenols are decyl dithiophosphoric acid, butyl isoheptyl dithiophostreated with metal oxides of hydroxides g-: Calcium phoric acid, butyl octadecyl dithiophosphoric acid, etc. drOXide Calcium Oxide) form the desired normal The salts of mixed diesters of dithiophosphoric id metal phenates, which phenates are then treated further are normally used in lubricating il compositions i with metal oxides and/or hydroxides and sulfur to form amounts sufiicient to inhibit oxidation of th b 11 the sulfurized basic metal phenate. On the other hand, Although it is preferred to use from 0.05% to 2.0% the phenols may be treated with metal oxides or hyby weight based on the final oil composition, lubricating droxides and sulfur in amounts sufficient to form the suloil concentrates containing as much as 50% or more by furized basic polyvalent metal phenate directly without weight may be prepared. the initial formation and separation of the normal sul- Zinc and calcium salts of mixed diesters of dithiofurized metal phenate.

In the preparation of basic sulfurized metal alltyl phenates, it is particularly preferred that the phenol, metal oxide or hydroxide, elemental sulfur and glycol be blended together for the reaction.

The amount of elemental sulfur present in the reaction mixture can vary from mole percent to 200 mole percent (based on the metal). It is preferred to use from 50 to 125 mole percent (based on the metal).

The amount of metal oxide or hydroxide used is that amount which will be sufficient to give the basic sulfurized metal phenate an amount of metal from 10% up to and greater than 100% more metal than that which is present in the normal metal phenate. The amount of metal oxide or hydroxide used in the reaction depends on the amount of metal oxide desired in the product in excess of that of the normal phenate, and, also depends on the Weight ratio of the glycol to metal oxide or hydroxide used. Normally, in the preparation of basic sulfurized metal phenates, a slight excess (e. g., 10 mole percent excess) of metal oxide or hydroxide is used in the reaction over that desired in the final basic phenate products.

The amount of glycol used will depend in part upon the nature of the glycol itself which is used, and, as noted 7 above, on the amount of metal oxide or hydroxide used.

In general, the use of lower molecular weight glycols (e. g., ethylene glycol) results in obtaining a higher yield of the basic phenate than does the use of glycols of higher molecular weight (e. g., propylene glycol) when both are used in the same amount by weight. The amount of glycol used is also governed by the solubility of the acidic substance (the phenols or the calcium phenates) and the metal oxides and hydroxides in the glycol.

preferred method for preparing basic sulfurized metal phenates is set forth in a Walker-Shiells U. S. aplication, Serial No. 210,522, filed February 12, 1951.

According to this method, oil-soluble basic sulfurized metal phenates are prepared by the reaction of phenols with metal oxides or hydroxides in the presence of ethylene glycol and sulfur.

The following examples illustrate the preparation of basic sulfurized metal phenates which are used according to the present invention to inhibit corrosion to silver caused by metal salts of mixed diesters of dithiophosphoric acids in lubricating oil compositions.

EXAMPLE 1 A mixture of 600 parts by weight of an alkyl phenol having a boiling range of 560 F. to 700 F, 140 parts by Weight of calcium hydroxide, 55 parts by weight of sulfur and 300 parts by weight of ethylene glycol was heated at 300 F. with agitation at an absolute pressure of 300 mm. of mercury. After the water of reaction had been distilled off, the pressure was reduced to 60 mm. of mercury and the temperature raised to 380 F., at which temperature and pressure the ethylene glycol was removed. During the period when the ethylene glycol was being removed, 400 parts by weight of petroleum lubricating oil were added. When all of the ethylene glycol had been removed, the mixture was cooled and 200 parts by weight of a petroleum thinner were added and the mixture was filtered. The filtrate was heated at re duced pressure to remove the petroleum thinner. The final lubricating oil composition contained 2.85% sulfur and 5.63% calcium, which was 92% more calcium than that present in a lubricating oil composition containing normal calcium allcyl phenate.

EXAMPLE 2 1 200 parts by weight of a petroleum lubricating oil having a viscosity of 49.5 SSU at 210 F.

At an absolute pressure of 16 mm. of mercury, the mixture was heated to distill off the water of reaction and'the ethylene glycol. During this time, an additional 200 parts by Weight of petroleum lubricating oil was added. The whole mixture was heated'to 380 F. at a pressure of 16 mm. of mercury in order to remove the ethylene glycol. After the product had been filtered, the reaction mixture contained 2.08% sulfur and 3.81% calcium. The final product contained 50% more calcium than that present in the corresponding normal sulfurized calcium alkyl phenate.

EXAMPLE 3 A mixture of 100 parts by weight of an alkyl phenol having a hydroxyl number of 150, 50 parts by weight of ethylene glycol, 20 parts by weight of calcium hydroxide, 8 parts by Weight of elemental sulfur, and 200 parts by weight of a petroleum lubricating oil was heated for 1 hour at a temperature of 380 to 400 F. and an absolute pressure of 50 to 60 mm. of mercury. This reaction mixture was filtered hot. The resulting petroleum lubricating oil composition contained 1.43% sulfur and 2.67% calcium, which was 60% more calcium than that present with the normal sulfurized calcium alkyl phenate.

EXAMPLE 4 A mixture of 100 parts by weight of alkyl phenol having a hydroxyl number of 140, 50 parts by weight of ethylene glycol, 200 parts by weight of a California solvent-refined naphthenic SAE lubricating oil, 20 parts by Weight of calcium hydroxide and 8 parts by weight of sulfur, was slowly heated at an absolute pressure of 50 to 60 mm. of mercury to a temperature of 380 F, at which temperature the mixture was stirred for 1 hour. The reaction mixture, after filtering, contained 2.26% calcium and 1.23% sulfur, which reaction mixture had more calcium than that present in a neutral sulfurized calcium alkyl phenate.

EXAMPLE 5 A mixture of 100 parts by weight of an alkyl phenol having a hydroxyl number of 140, parts by weight of ethylene glycol, 200 parts by weight of a California solvent-refined naphthenic SAE 30 lubricating oil, 22

- parts by weight of calcium hydroxide and 8 parts by weight of sulfur was slowly heated at an absolute pressure of 50 to mm. of mercury to a temperature of 380 F., at which temperature the mixture was stirred for 1 hour. The reaction mixture, after filterin contained 2.48% calcium and 1.20% sulfur, which reaction product had 60% more calcium than that present in a hen? tral sulfurized calcium phenate.

EXAMPLE 6 A mixture of parts by weight =31 an alkyl phenol having a hydroxyl number of 132, 18 parts by weight of calcium oxide, 50 parts by weight of ethylene glycol, 9.5

furized calcium alkyl phenate.

in order to evaluate the effectiveness of basic sulfurized metal phenates for inhibiting corrosion due to metal salts of mixed diesters of dithiophosphoric acids, Silver Strip Corrosion Tests were made on the lubricating oil compositions of this invention. These Silver Strip Corrosion Tests were performed as follows:

A silver metal strip having the dimensions of 2 /2 inches x %1 inch x inch was first cleaned with a wire brush until the strip was highly polished. The strip was weighed and the weight recorded. This highly polished silver strip was then placed in a 600 ml. beaker in such a manner that the strip was completely immersed when 300 gms. of the oil being tested were poured into the beaker. The oil was stirred at a temperature of 300 F. for 20 hours, at which time the silver strip was removed and cleaned, first with colorform, then with petroleum ether. The appearance of the strip was noted. Those strips which had been severely attacked were quite black. The tested silver strips were washed in 15% aqueous solution of potassium cyanide for about 5 minutes to remove the sulfide film adhering to the strip. After the strip had been washed with the potassium cyanide and dried, it was weighed. The difference in the weight of the original strip and the strip after the potassium cyanide wash was noted and recorded as the weight loss due to corrosion by the polyvalent metal salt of the esters of dithiophosphoric acids.

The data presented hereinbelow shows the effectiveness of basic metal salts of phenol in reducing corrosion to silver by metal salts of mixed diesters of dithiophosphoric acids. The data were obtained according to the described Silver Strip Test. The reference oil used in obtaining these data was a California solvent-refined naphthenic base SAE 30 base oil to which was added 0.6 millimole percent of a zinc salt of a mixed diester of a dithiophosphoric acid prepared as follows:

A mixture of 237 parts by weight (77 mole percent) of secondary butyl alcohol, 98 parts by weight (23 mole percent) of methylisobutylcarbinol and 222 parts by weight of P255 was charged to a reaction vessel and agitated at 170 F. for a period of 2 hours. The reaction mixture was cooled and filtered to remove a small amount of unreacted P285. The resulting butyl methylisobutylcarbinol dithiophosphate reaction product was a dark, red-green liquid having a neutralization number of 193 (Mgs. KOH/gm., a viscosity of 35.7 SSU at 100 F., and contained 24.0% sulfur and 11.9% phosphorus.

To the above mixture was added 87 parts by Weight of zinc oxide, after which the whole was heated with agitation at 130 F. for 4 hours until a pH of 6.7 was reached. After the Water of neutralization had been removed, the oil solution contained 7.6% zinc, 7.2% phosphorus and 15.0% sulfur.

Table I [Basic phenate used was that of Example 4 above] Percent Calcium 222? Test Lube Oil Composition (by Test,"

Wt. Loss Phenate in 1 Reference Oil 0. 0 19 t. 4 2 Reference Oil+2.0 millirnole percent 0.08 3.9

basic phenate. 3 Reference Oil+1.0 milliniole percent 0.04 1.5

basic phenate. 4 Reference Oil-{-05 millimole percent 0.02 1.9

basic phenate. 5 Reference Oil+0.25 millimolc percent 0.01 2.1

basic phenate. l 1

Table II [Basic phenate used was that of Example 5 above] Percent Calcium gfi k Lube Oil Composition g g' Test,"

Basic g' i Phenate g I l 1 Reference Oil 0.0 194.4 Reference Oil +3.0 millirnolc percent 0. 12 12. 2

basic phenate. Reference Oil +2.0 millirnole percent 1 0.08 2.1

basic phenate. r 4 Reference Oil +1.0 millimole percent i 0.04 2 5 basic phenate. 5 Reference Oil +0.25n1illimole percent 0. 01 1 2. 3

basic phenate.

1 This reference oil was the same as that of Table 1.

8 Table I ll [Basic phenate used was that of Example 6 above] 1 This reference oil was the same as that of Example 1.

As stated hereinabove, in the lubricating oil composition of this invention, it is preferred that basic sulfurized metal phenates be present in smaller amounts than metal salts of mixed diesters of dithiophosphoric acids. Thus, it is preferred that the ratio (by weight) of basic sulfurized metal phenates to metal salts of mixed diesters of dithiophosphoric acids have a value of 1, or less than 1, preferably from 0.5 to 1.

In addition to the additives already presented above, lubricating oil compositions contemplated herein may contain other agents, such as pour point depressants, oiliness agents, extreme pressure agents, blooming agents, compounds for enhancing the viscosity index of the lubricating oil, grease-forming agents, peptizing agents, detergents, etc.

I claim:

1. A lubricating oil composition comprising a major proportion of an oil of lubricating viscosity having incorporated therein a small amount, sufficient to inhibit oxidation, of a metal salt of a mixed diester of dithiophosphoric acid, wherein one ester group is an alkyl radical having from 1 to 4 carbon atoms, and another ester group is an alkyl radical having from 6 to 18 carbon atoms, and said metal being selected from the group of zinc and calcium, and, in addition, a smali amount, sufficient to inhibit the corrosion to silver caused by said metal salt of dithiophosphoric acid, of a basic sulfurized metal salt of an alkyl phenol having a metal selected from the group consisting of calcium and barium, wherein the metal of said phenol is present in an amount at least 10% in excess of that required to form a neutral phenate.

2. The lubricating oil composition of claim 1, wherein said metal salt of a mixed diester of dithiophosphoric acid ester contains one alkyl radical having from 1 to 4 carbon atoms, and another alkyl radical having from 6 to 10 carbon atoms. I

3. The lubricating oil composition of claim 1, wherein said metal salt of mixed diester of dithiophosphoric acid is a zinc salt, and wherein said metal salt of a phenol is a calcium salt.

4. The lubricating oil composition of claim 1, wherein said metal salt of mixed diester of dithiophosphoric acid is a zinc salt, and wherein said metal salt of a phenol is a barium salt.

5. A lubricating oil composition comprising a major proportion of an oil of lubricating viscosity, from 0.05% to 2% by weight of a metal salt of a mixed diester of dithiophosphoric acid, one ester group being an alkyl radical having from 1 to 4 carbon atoms, and another ester group being an alkyl radical having from 6 to 18 carbon atoms, said metal selected from the group consisting of zinc and calcium, and a basic sulfurized metal phenate in an amount sufiicient to inhibit the corrosion to silver caused by said metal salt of dithiophosphoric acid, said basic phenate having a metal selected from the group of calcium and barium wherein the metal of said phenate is present in an amount at least 10% in excess of that required to form a neutral phenate, such that the ratio of basic sulfurized metal phenate to metal salt of mixed diester of dithiophosphoric acid will have a value less than 1.

6. A lubricating oil composition comprising a major proportion of an oil of lubricating viscosity, from 0.05% to 2% by weight of a metal salt of a mixed diester of dithiophosphoric acid, one ester group being an alkyl radical having from 1 to 4 carbon atoms, and another ester group being an alkyl radical having from 6 to 18 carbon atoms, said metal selected from the group consisting of zinc and calcium, and a basic sulfurized calcium alkyl phenate in an amount sutiicient to inhibit the corrosion to silver caused by said metal salt of dithiophosphoric acid, which amount of basic phenate is such that the ratio of basic phenate to metal salt of mixed diester of dithiophosphoric acid will have a value less than 1, said metal of said phenate being present in amounts at least 10% in excess of that required to form a neutral phenate.

7. A lubricating oil composition comprising a major proportion of a lubricating oil containing from 0.05 to 2% by Weight of the zinc salt of a mixed diester of dithiophosphoric acid, said diester being obtained by reacting phosphorus pentasulfide with a blend consisting of two different monohydric alcohols, one of said alcohols containing not more than 4 carbon atoms, and the other of said alcohols containing from 6 to 10 carbon atoms, to which lubricating oil is added a basic sulfurized metal phenate having a metal selected from the group consisting of calcium and barium, such that the ratio of basic phenate to zinc salt will have a value less than 1, said basic phenate being present in the final composition in an amount suflicient to inhibit corrosion to silver caused by said zinc salt, and wherein the metal of said phenate is present in amounts of at least 10% in excess of that required to form the neutral metal phenate.

8. The lubricating oil composition of claim 7, wherein one of said monohydric alcohols is sec.-butyl alcohol, and the other of said monohydric alcohols is methylisobutylcarbinol, and wherein the ratio of basic phenate to zinc salt has a value from 0.5 to 1.0.

9. The lubricating oil composition of claim 7, wherein one of said alcohols contains not more than 4 carbon atoms, and wherein the other of said alcohols contains from 6 to 18 carbon atoms and wherein the ratio of basic phenate to zinc salt has a value from 0.5 to 1.0.

10. The lubricating oil composition of claim 7, wherein the basic sulfurized polyvalent metal phenate is a basic sulfurized calcium alkyl phenate.

11. The lubricating oil composition of claim 6, wherein the basic sulfurized polyvalent metal phenate is a basic sulfurized barium alkyl phenate 12. A lubricating oil composition comprising a major proportion of a lubricating oil containing from 0.05 to 2% by weight of the zinc salt of a mixed diester of dithiophosphoric acid, said diester being obtained by reacting phosphorus pentasulfide with a blend consisting of two ditferent monohydric alcohols, one of said alcohols containing not more than 4 carbon atoms, and the other of said alcohols containing from 6 to 18 carbon atoms, to which lubricating oil is added a basic sulfurized metal phenate in an amount sufiicient to inhibit corrosion to silver caused by said zinc salt, said metal phenate having a metal selected from the group consisting of calcium and barium, such that the ratio of basic phenate to zinc salt will have a value less than 1, and wherein the metal of said phenate is present in an amount at least 10% in excess of that required to form a neutral phenate.

13. A lubricating oil composition comprising a major proportion of a lubricating oil containing from 0.05% to 2% by weight of the calcium salt of a mixed diester of dithiophosphoric acid, said diester being obtained by reacting phosphorus pentasulfide with a blend consisting of two different monohydric alcohols, one of said alcohols containing not more than 4 carbon atoms, and the other of said alcohols containing from 6 to 18 carbon atoms, to which lubricating oil is added a basic sulfurized metal phenate in an amount sufiicient to inhibit corrosion to silver caused by said calcium salt, said metal phenate having a metal selected from the group consisting of calcium and barium, such that the ratio of basic phenate to zinc salt will have a value less than 1, and wherein the metal of said phenate is present in an amount of at least 10% in excess of that required to form a neutral phenate.

References (Iited in the file of this patent UNITED STATES PATENTS 2,406,564 Rogers et al Aug. 27, 1946 

1. A LUBRICATINS OIL COMPOSITION COMPRISING A MAJOR PROPORTION OF AN OIL OF LUBRICATING VISCOSITY HAVING INCORPORATED THEREIN A SMALL AMOUNT, SUFFICIENT TO INHIBIT OXIDATION, OF A METAL SALT OF A MIXED DIESTER OF DITHIOPHOSPHORIC ACID, WHEREIN ONE ESTER GROUP IS AN ALKYL RADICAL HAVING FROM 1 TO 4 CARBON ATOMS, AND ANOTHER ESTER GROUP IS AN ALKYL RADICAL HAVING FROM 6 TO 18 CARBON ATOMS, AND SAID METAL BEING SELECTED FROM THE GROUP OF ZINC AND CALCIUM, AND, IN ADDITION, A SMALL AMOUNT, SUFFICIENT TO INHIBIT THE CORROSION TO SILVER CAUSED BY SAID METAL SALT OF DITHIOPHOSPHORIC ACID, OF A "BASIC" SULFURIZED METAL SALT OF AN ALKYL PHENOL HAVING A METAL SELECTED FROM THE GROUP CONSISTING OF CALCIUM AND BARIUM, WHEREIN THE METAL OF SAID PHENOL IS PRESENT IN AN AMOUNT AT LEAST 10% IN EXCESS OF THAT REQUIRED TO FORM A NEUTRAL PHENATE. 